The present invention relates to a process for preparing (cyclo)aliphatic diisocyanates and triisocyanates by the phosgenation of (cyclo)aliphatic diamines and triamines in the gas phase.
It is known that diamines can be phosgenated in the gas phase. The phosgenation of (cyclo)aliphatic diamines in a tubular reactor equipped with a mechanical stirrer is described in GB-A 1 165 831. The reactor resembles a film evaporator in which the stirrer mixes the gases and at the same time brushes over the heated walls of the tubular reactor, in order to prevent a build-up of polymeric material on the wall of the pipe. However, the use of a high-speed stirrer when handling phosgene at a temperature of approximately 300xc2x0 C. necessitates great expense on safety measures to seal the reactor and retain the stirrer in the highly corrosive medium.
EP-A 0 289 840 and EP-A 0 749 958 describe the phosgenation of (cyclo)aliphatic diamines using a cylindrical reaction chamber without moving parts, in which the reactants are reacted with one another while a turbulent flow is maintained. The management of the flow leads to back-mixing as a result of which the products react with the diamine starting material to form solid deposits. This leads to contamination of the reactor and blockages in the path of the gas.
It is an object of the present invention to produce (cyclo)aliphatic isocyanates by the gas-phase phosgenation of the corresponding amines while avoiding the previously mentioned disadvantages of prior art.
This object may be achieved with the process of the present invention by carrying out the reaction such that the flow of at least one of the reactants is accelerated in the region where the reactants are mixed together.
The present invention relates to a process for preparing a (cyclo)aliphatic diisocyanate or triisocyanate corresponding to the formula
Rxe2x80x94(NCO)nxe2x80x83xe2x80x83(I),
wherein
R represents a (cyclo)aliphatic hydrocarbon group having up to 15 carbon atoms, provided that there are at least two carbon atoms between two nitrogens,
n represents the number 2 or 3, by
a) separately heating phosgene and a diamine or a triamine corresponding to the formula
Rxe2x80x94(NH2)nxe2x80x83xe2x80x83(II),
xe2x80x83to a temperature of 200xc2x0 C. to 600xc2x0 C., wherein the amine may optionally be diluted with an inert gas or with the vapors of an inert solvent,
b) accelerating the flow of at least one of the reactants in the region where the reactants are mixed and
c) continuously reacting the reactants in a reaction chamber that does not have moving parts.